skip initramfs check
PATCH 1/1 skip initramfs check
Hi,
The initramfs check at populate_rootfs() can consume significant time (several seconds) on slow/embedded platforms, since it has to decompress the image.
Add an option to skip it under CONFIG_EMBEDDED.
Is there a nicer way to achieve the same result?
init/Kconfig +10 -0
@@ -398,6 +398,16 @@ config CC_ALIGN_JUMPS no dummy operations need be executed. Zero means use compiler's default. +config INITRAMFS_SKIP + bool "Skip initramfs verification of initrd" if EMBEDDED + default n + help + By default the initialization code uncompresses the initrd image to + verify if it is a initramfs image. + + Say Y here if you are sure not to be using initramfs and want to + skip that test. + endmenu # General setup config TINY_SHMEM
init/initramfs.c +2 -0
@@ -486,6 +486,7 @@ void __init populate_rootfs(void)if (initrd_start) {int fd;printk (KERN_INFO "checking if image is initramfs..." ); +#ifndef CONFIG_INITRAMFS_SKIP err =unpack_to_rootfs ((char *)initrd_start, initrd_end - initrd_start,1 );if (!err) {
@@ -495,6 +496,7 @@ void __init populate_rootfs(void)free_initrd (); return; } +#endif printk ("it isn't (%s); looks like an initrd\n" , err); fd =sys_open ("/initrd.image" ,O_WRONLY |O_CREAT ,700 );if (fd >=0 ) {
Quoted 8 lines · Marcelo Tosatti
The initramfs check at
populate_rootfs()can consume significant time (several seconds) on slow/embedded platforms, since it has to decompress the image.Add an option to skip it under
CONFIG_EMBEDDED.Is there a nicer way to achieve the same result?
I'd have thought that a __setup option would be preferable? Remove an ifdef, more flexible, and it's all __init code anyway.
Quoted 5 lines · Marcelo Tosatti
Hi,
The initramfs check at
populate_rootfs()can consume significant time (several seconds) on slow/embedded platforms, since it has to decompress the image.
Query: is the problem that a big initramfs image is being unpacked more than once, or is unpacking an empty initramfs image (134 bytes) causing a significant delay?
I'm fairly certain that back in 1990 I could unzip 134 bytes on my 33 mhz 386 running dos in a fraction of a second. What's the use case here?
Rob
Hi Rob,
Quoted 10 lines · Rob Landley
Quoted 5 lines · Marcelo Tosatti
Hi,
The initramfs check at
populate_rootfs()can consume significant time (several seconds) on slow/embedded platforms, since it has to decompress the image.Query: is the problem that a big initramfs image is being unpacked more than once, or is unpacking an empty initramfs image (134 bytes) causing a significant delay?
The problem is a big non-initramfs RAMDISK image (used for root mountpoint on this particular embedded platform), that is decompressed more than once:
- during the initramfs check, which fails because it is not initramfs.
- during the real RAMDISK decompression to memory.
Quoted 2 lines
I'm fairly certain that back in 1990 I could unzip 134 bytes on my 33 mhz 386 running dos in a fraction of a second. What's the use case here?
So the issue is not the empty initramfs image (which BTW could probably be made unecessary?), but a 10Mb RAMDISK image being decompressed by a 48Mhz PPC, which takes quite a few seconds.
Need to rework the patch to use a __setup option as Andrew suggested.
Quoted 11 lines · Marcelo Tosatti
Hi Rob,
Quoted 3 lines
Query: is the problem that a big initramfs image is being unpacked more than once, or is unpacking an empty initramfs image (134 bytes) causing a significant delay?
The problem is a big non-initramfs RAMDISK image (used for root mountpoint on this particular embedded platform), that is decompressed more than once:
- during the initramfs check, which fails because it is not initramfs.
- during the real RAMDISK decompression to memory.
Quoted 8 lines
Quoted 2 lines
I'm fairly certain that back in 1990 I could unzip 134 bytes on my 33 mhz 386 running dos in a fraction of a second. What's the use case here?
So the issue is not the empty initramfs image (which BTW could probably be made unecessary?), but a 10Mb RAMDISK image being decompressed by a 48Mhz PPC, which takes quite a few seconds.
Need to rework the patch to use a
__setupoption as Andrew suggested.
It sounds to me like is the initial check (which is just giving a thumbs up/thumbs down "is this an initramfs", correct?) only needs to decompress the first page or so of data to make this determination. A quick glance at the code seems to imply it's just checking the header and the first entry, so 4k should be plenty for that.
Some variant of lib/zlib_inflate... Ouch, bit of a mess there. Hey Matt: you know this area. Is it feasible to do some kind of:
deflate_init(whatever)deflate_next_x_bytes(source *, dest *, length)
To grab a the first X bytes from the initramfs image?
Rob
Quoted 27 lines · Rob Landley
Quoted 11 lines · Marcelo Tosatti
Hi Rob,
Quoted 3 lines
Query: is the problem that a big initramfs image is being unpacked more than once, or is unpacking an empty initramfs image (134 bytes) causing a significant delay?
The problem is a big non-initramfs RAMDISK image (used for root mountpoint on this particular embedded platform), that is decompressed more than once:
- during the initramfs check, which fails because it is not initramfs.
- during the real RAMDISK decompression to memory.Quoted 8 lines
Quoted 2 lines
I'm fairly certain that back in 1990 I could unzip 134 bytes on my 33 mhz 386 running dos in a fraction of a second. What's the use case here?
So the issue is not the empty initramfs image (which BTW could probably be made unecessary?), but a 10Mb RAMDISK image being decompressed by a 48Mhz PPC, which takes quite a few seconds.
Need to rework the patch to use a
__setupoption as Andrew suggested.It sounds to me like is the initial check (which is just giving a thumbs up/thumbs down "is this an initramfs", correct?) only needs to decompress the first page or so of data to make this determination. A quick glance at the code seems to imply it's just checking the header and the first entry, so 4k should be plenty for that.
Quoted 7 lines
Some variant of
lib/zlib_inflate... Ouch, bit of a mess there. Hey Matt: you know this area. Is it feasible to do some kind of:
deflate_init(whatever)deflate_next_x_bytes(source *, dest *, length)To grab a the first X bytes from the initramfs image?
Not at the moment. But I think it is feasible to simply move the ramdisk detection and unpacking inside the ramfs state machine. In other words, add two new states:
- detecting type
- unpacking ramdisk
When the first few bytes are fed from the decompressor to the state machine, we either transition to the normal ramfs unpacking or we treat it as a ramdisk.
Signature · 1 line
Mathematics is the supreme nostalgia of our time.
Quoted 40 lines · Matt Mackall
Quoted 27 lines · Rob Landley
Quoted 11 lines · Marcelo Tosatti
Hi Rob,
Quoted 3 lines
Query: is the problem that a big initramfs image is being unpacked more than once, or is unpacking an empty initramfs image (134 bytes) causing a significant delay?
The problem is a big non-initramfs RAMDISK image (used for root mountpoint on this particular embedded platform), that is decompressed more than once:
- during the initramfs check, which fails because it is not initramfs.
- during the real RAMDISK decompression to memory.Quoted 8 lines
Quoted 2 lines
I'm fairly certain that back in 1990 I could unzip 134 bytes on my 33 mhz 386 running dos in a fraction of a second. What's the use case here?
So the issue is not the empty initramfs image (which BTW could probably be made unecessary?), but a 10Mb RAMDISK image being decompressed by a 48Mhz PPC, which takes quite a few seconds.
Need to rework the patch to use a
__setupoption as Andrew suggested.It sounds to me like is the initial check (which is just giving a thumbs up/thumbs down "is this an initramfs", correct?) only needs to decompress the first page or so of data to make this determination. A quick glance at the code seems to imply it's just checking the header and the first entry, so 4k should be plenty for that.
Quoted 7 lines
Some variant of
lib/zlib_inflate... Ouch, bit of a mess there. Hey Matt: you know this area. Is it feasible to do some kind of:
deflate_init(whatever)deflate_next_x_bytes(source *, dest *, length)To grab a the first X bytes from the initramfs image?
Not at the moment. But I think it is feasible to simply move the ramdisk detection and unpacking inside the ramfs state machine. In other words, add two new states:
Quoted 6 lines
- detecting type
- unpacking ramdiskWhen the first few bytes are fed from the decompressor to the state machine, we either transition to the normal ramfs unpacking or we treat it as a ramdisk.
Yes that would be ideal.